aerosol influence on temperature 
Source: Hadley Centre Hadcm3 climate model.
The graph gives the difference in temperature in the period 1990-1999 caused by ozone depletion and aerosols.
Ozone depletion has its largest influence near Antarctica, aerosols mostly in the NH.

The most important influence of aerosols is downwind SO2 sources, which comprise some 10% of the earth's surface. The global influence of aerosols is app. 0.5 ºC, according to the models. That means that the total in the regions of interest must have an influence of around 5 ºC. The HADcm3 model locates the zone with the largest influence at the Finnish-Russian border. In this case, it is the zone where the largest change in temperature should be seen, due to the reduction of (especially sulfate) aerosols in Europe.

The reduction in sulfate emissions in Europe is huge. Since 1975, a reduction of over 50% is achieved. That should be visible at the place with the highest impact as a temperature increase since the reduction started. For the 1990-1999 period the reduction is app. 40%:

SO2 emissies Europa
Source: UNEP
SO2 emissions in million tons per year.


station trends
Source: GISS database.

The stations were as far as possible rural one's in three groups: East is in the modeled zone in Europe (near the Finnish-Russian border) where the largest influence (4-6 ºC) should be seen in the period 1975-1990, when the anthropogenic SO2 emissions more than halved (-56%) . Middle is the zone with a medium influence (2-4 ºC at South Scandinavia/North Germany), and West is Ireland/South England (0-2 ºC).

The stations choosen from the GISS database are:
East: Vytegra, Reboly, Kajaani, Jyvaskyla (average 62.9N, 30.2E)
Middle: Visby, Leba, Lindenberg, Oslo Gardermo (marked as rural!), Schleswig-Jag (average 57.7N, 14.1E)
West: Lerwick, Shannon airport, Belmullet, Valentia obs. (average 54.7N, 7.6W)

No influence is measurable in the surface trends at or around the locations with the highest impact, compared to less contaminated area's like South England or Ireland. Obvious in the trends is the influence from land/sea climate and the influence of the NOA in the different stations.

As one can see, the largest difference in temperature in the middle and East zone's is some 2 ºC, while in the West zone it still is 1 ºC. Far less than what the model calculated. Even if we accept that the full difference in temperature is from less SO2 emissions, that means that the global influence is at maximum 0.1 ºC. But even that is questionable, as the NAO has a distinct jump in 1990 to strong positive, the same year that the temperatures in all three trends show a jump. The difference between the West trend and the two other trends can be explained by the damping influence from the oceans.

To make a comparison, here the NAO trend:

NAO trend
Source: Hurrell


The influence of aerosols in current models is largely overestimated. Consequently: to fit the past trends, especially the 1945-1975 period, the models need to reduce the influence of GHGs on temperature. That besides the point that they probably underestimate solar influences too.

On the net: 21 November, 2004.
Last update: 31 October, 2011.

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